Those skilled in the art are familiar with the principles of windshear and windshear warning systems. For example, there are U.S. Pat. Nos. 3,892,374; 4,053,883 and 4,593,285. These systems are basically "reactive" systems because they cannot sense conditions ahead of the flight path of the aircraft; in that sense, these systems are not predictive or anticipatory of a dangerous windshear condition. They utilize sensors aboard the aircraft to compute air mass acceleration and inertial acceleration, in order to provide a warning of a dangerous windshear condition. Because they are "reactive", they provide a warning only after the aircraft has entered a dangerous downdraft or microburst situation. Thus, these prior art systems provide a short time for the pilot to safely maneuver the aircraft.
Heretofore, warning threshold of a windshear warning system has been established or set as a function of the climb performance of the aircraft. For example, in the case of the Boeing 737 aircraft, the warning threshold is set at approximately 150 mgs (i.e., 1000 mgs=32 ft/sec.sup.2); the Boeing 747 aircraft has a setting of approximately 80 mgs (both vertical and horizontal windshear or components thereof). Such threshold settings are basically a compromise between giving a reasonable and timely alert and avoiding nuisance warnings due to mild gusts or slightly turbulent conditions, such as ground turbulence, which may be encountered during a normal take-off and landing. Preferably, a windshear warning system should distinguish between a deadly convective flow (such as a "microburst") and a Fall, windy day when a cold front has recently passed through the area. More importantly, a windshear warning system should anticipate a dangerous condition, rather than simply become responsive to it. A windshear warning system that would not only provide adequate warning but also take in consideration special conditions at the airport of interest, including seasonal and geographic conditions would prove to be a significant contribution to the art and an important advance in flight safety.